The present invention relates to a sealing device intended particularly, but not exclusively, for carpules or injection cartridges, in particular those containing anesthetics.
These cartridges, for mounting on a syringe, are constituted by a small tube, generally made of glass having an end wall that constitutes a moving piston for expelling liquid into a hollow needle. Prior to the needle being inserted, the front portion of the cartridge is closed by a rubber capsule or seal membrane disk through which the needle is to pass, the seal membrane being secured to the tube by means of a metal ring crimped over the seal membrane and onto the front of the tube.
Such a structure provides acceptable sealing during storage and transport of cartridges, with pressure being in balance on either side of the membrane. However, it is frequently observed that when pressure is applied to the end of the cartridge, once a needle has been mounted on the cartridge, then a leak occurs between the seal membrane disk and the metal ring. This leak takes place at the periphery of the rubber membrane and the metal ring. The pressure applied to the end of the carpule is transmitted by the liquid which tends to lift the membrane disk off the seat constituted by the front portion of the tube, thus allowing the liquid to pass between the seat and the rear wall of the membrane.
Proposals have already been made to improve the sealing of cartridges provided with sealing means so as to ensure that the content remains sterile.
AU-A-603 862 describes a crown that serves to center the rubber membrane.
In U.S. Pat. No. 1,993 629, a collar deforms a block of rubber that closes the front of the glass tube.
In U.S. Pat. No. 2 157 503, a collar has an acute-angled section, but neither its function nor its dimensional relationships with the tube are defined.
Those three documents relate to the hand-operated syringes, i.e. acting under relatively low pressure.
The object of the invention is to mitigate the drawbacks mentioned above even when high pressure is applied, and to make injections possible without leaks, even when high pressures are necessary, e.g., for intradiploic, intraligamentary, intraseptal, intrapalatine, etc. injections. It is based on the idea that to provide sealing under high pressure it is necessary to compress a flexible membrane between the edges of two non-deformable parts.
According to the invention, in the device for sealing a syringe in which there is inserted a cartridge that is closed at its top end by a flexible membrane and that is connected to an injection needle, the link part between the needle and the front portion of the cartridge presents a projecting crown of diameter substantially equal to the diameter of the opening in the cartridge, and preferably slightly smaller than opening in the cartridge, that comes to bear against the flexible membrane so as to press it against the inside edge of the top surface of the cartridge.
Thus, when pressure is applied to the end wall of the carpule, the crown presses the disk strongly against the top edge of the opening, thereby deforming it and preventing any leakage. The connection part between the needle and the cartridge can either be an adapter for mounting the needle on a syringe or needle carrier, or else an overmolded plastic part that surrounds the needle proper. With some syringes, the needle carrier integrated in the front portion by molding can have the same disposition.